A known inkjet printing apparatus for printing on a plurality of sheets comprises a conveying belt unit and a print station comprising an inkjet print head assembly for applying droplets of ink on the sheets.
The conveying belt unit comprises a transport belt and several rollers arranged for transporting the endless transport belt in a conveying direction along the print station. The endless transport belt comprises a support surface for supporting the plurality of sheets during transport along the print station. The support surface comprises perforations arranged for allowing a suction force to hold each of the plurality of sheets on the support surface. A suction device is arranged comprising a vacuum chamber arranged for applying the suction force to the perforations of the support surface in order to attract each of the plurality of sheets on the support surface. A first sheet and a second sheet are arranged on the support surface at a standard sheet-to-sheet distance between one another. In the area of the sheet-to-sheet distance the perforations are not covered by the sheets.
During printing by the print head assembly, droplets of ink are applied on the sheet in order to form an image. The ink may be an aqueous ink and/or may be any other solvent containing ink. When droplets of an aqueous ink are applied on the sheet evaporation of the water component may occur, thereby increasing the humidity of the air present in a print region between the print head assembly and the support surface.
In case the moisture in the air becomes saturated in the print region, dew may form on one or more print heads of the print head assembly at a dew point depending on the temperature of the respective print head. Typically the temperature of the print heads is controlled to be substantially constant during printing in order to control the ink droplet formation. In any way, dew formation on the print head may disturb the ink droplet formation during printing, which leads to image defects.
It is known to detect a dew point of the air in the print region by measuring a temperature of the air and measuring the humidity of the air of the print region. Subsequently the temperature of the air in the print region may be increased and/or the air may be moved by an additional air conditioning unit in the print region in order to prevent dew formation on the print head assembly.
A disadvantage of this method is that, in order to prevent the dew formation on the print head assembly, sensors for measuring air temperature and air moisture are needed and the air conditioning unit is needed to move the air and/or heat the air in the print region in response to the sensed air temperature and air moisture.